Electrical connectors are known that include housings and a plurality of terminals arranged in a grid array of terminals typically arranged in multiple rows and columns. Often the connector is then mounted to a circuit board or back plane and the terminals are conventionally connected to conductive traces thereof by their contact sections being soldered thereto. Generally the circuit board or back plane must also accommodate means for securing the housing to the board, which requires some space around the grid array. With the increasing need miniaturization as well as the need to increase the capabilities of electronic devices, space on circuit board and back planes is at a premium.
It is therefore desirable to minimize the amount of space required for grid array of terminals.
It is further desirable to provide a method for securing the terminals in grid arrays to a circuit board without the need to expose all of the components thereon to the high temperature required by wave soldering and the like.
U.S Pat. No. 4,852,252 discloses providing each of the terminals of a connector with a thin layer of magnetic material along the surface of the nonmagnetic low resistance solder tail of the terminal facing away from the surface to which a wire end will be soldered; in U.S. Pat. No. 4,995,838 a preform of foil having a magnetic layer is disclosed to be soldered to the terminal solder tail's wire-remote surface. The bimetallic structure uses the Curie temperature of the magnetic material to define an article which will generate thermal energy when subjected to radio frequency current of certain frequency for sufficient short length of time until a certain known temperature is achieved, above which the structure is inherently incapable of rising; by selecting the magnetic material and sufficient thickness thereof and selecting an appropriate solder, the temperature achieved can be selected to be higher than the reflow temperature of the solder preform; when the terminal is subjected through induction to RF current of the appropriate frequency, the solder tail will generate heat which will radiate to the solder preform, reflow the solder, and be conducted along the wire and the terminal and radiate further to shrink the tubing and melt the sealant material. The terminal thus includes an integral mechanism for enabling simultaneous soldering and sealing without other application of heat; excess heat is avoided as is the potential of heat damage to remaining portions of the connector or tubing.
Another U.S. Pat. No. 4,789,767 discloses a multipin connector whose contacts have magnetic material layers on portions thereof spaced from the contact sections to be surface mounted to respective traces on the surface of a printed circuit board. An apparatus is disclosed having a coil wound magnetic core having multiple shaped pole pieces in spaced pairs with an air gap therebetween within which the connector is placed during soldering. The pole pieces concentrate flux in the magnetic contact coating upon being placed beside the contact sections to be soldered, to transmit RF current to each of the contacts, generating thermal energy to a known maximum temperature to reflow the solder and join the contact sections to the conductive traces of the printed circuit element.
Such Curie point heating is disclosed in U.S. Pat. Nos. 4,256,945; 4,623,401; 4,659,912; 4,695,713; 4,701,587; 4,717,814; 4,745,264 and European Patent Publication No. 0241,597. When a radio frequency current for example is passed through such a bipartite structure, the current initially is concentrated in the thin high resistance magnetic material layer which causes heating; when the temperature in the magnetic material layer reaches its Curie temperature, it is known that the magnetic permeability of the layer decreases dramatically; the current density profile then expands into the non-magnetic substrate of low resistivity. The thermal energy is then transmitted by conduction to adjacent structure such as wires and solder which act as thermal sinks; since the temperature at thermal sink locations does not rise to the magnetic material's Curie temperature as quickly as at non-sink locations, the current remains concentrated in those portions of the magnetic material layer adjacent the thermal sink locations and is distributed in the low resistance substrate at non-sink locations. It is known that for a given frequency the self-regulating temperature source thus defined achieves and maintains a certain maximum temperature dependent on the particular magnetic material. One source for regenerating radio frequency current such as of 13.56 mHz is disclosed in U.S. Pat. No. 4,626,767.
The conductive substrate can be copper having a magnetic permeability of about one and a resistivity of about 1.72 micro-ohm-centimeters. The magnetic material may be for example a clad coating of nickel-iron alloy such as Alloy No. 42 (42% nickel, 58% iron) or Alloy No. 42-6 (42% nickel, 52% iron and 6% chromium). Typical magnetic permeabilities for the magnetic layer range from fifty to about one thousand, and electrical resistivities normally range from twenty to ninety micro-ohm-centimeters as compared to 1.72 for copper; the magnetic material layer can have a Curie temperature selected to be from the range of between about 200.degree. C. to about 500.degree. C., for example. The thickness of the magnetic material layer is typically one to two skin depths; the skin depth is inversely proportional to the square root of the product of the magnetic permeability of the magnetic material and the frequency of the alternating current passing through the two-layer structure. Solders can be tin-lead such as for example Sn 63 reflowable at a temperature of about 183.degree. C. or Sb-5 reflowable at a temperature of about 240.degree. C. Generally it would be desirable to select a Curie temperature of about 15.degree. C. to 75.degree. C. above the solder reflow temperature.